your question is vague. Help in what? topic, research proposal, advice on where or how to apply? choosing field. It is unlikely to get an answer with such no details of what you want.

Theoritically yes. I have done it twice when asked to provide my Master thesis during the interview. But if he/she did not ask you for further documents, I think it would indicate a sign of weakness. In my opinion, their decision will not change based on your document if they have not asked particular for it.

It could be helpful if you share here why you are having a hard time. I had a bad experience in my PhD and I might spot the real bad signs and the "normal" bad signs.

Hi. Of course you can. Actually I would encourage you to do so. Do not get stuck in a PhD you do not like.

Hello.
First you have to find a supervisor who is happy to supervise you and happy to help you to apply for appropriate funding either in Uni or councils. To be honest, you will hear a lot "I am happy with your application but I have no funding available". Also for non EU students, it is far more complicated. Everyone wants to go to the UK to do a PhD while the funding is limited

Hi. I agree that addressing someone with name and no greeting is actually rude (not seeming rude). If I were you I would just use Hi/Hello first name. It is waht I think is best available response.
Be ware of something. Email communication is usually more rude than normal talk. I try to contact the persons personally or by phone first. of course this is not applicable in many cases such as yours. Also I found out that sometimes whatsapp group message communications tend to be less polite and less friendly than normal communications. It is just like that so try not to get offended (Sometimes I try and fail :)).

Is your PhD fully funded? Do you need the job financially as a full time? If your PhD is fully funded, I woud agree with ncrbrts to try to work less hour for less salary. If not possible, I would recommend to take a retail job.
Career wise it would be nice, but you tried it and believe me, there is no good coming from what you describe.

Hello. First congratulations for getting something worth published in peer reviewed journal in Bachelor's work. It is really something.
The situation you described is not easy and you know it. I think you can only reposnd saying that this analysis was outside the scope of work. If the reviewer think it is mandatory to accept the paper, there is nothing you can do to convince him.
The second alternative is to submit to another journal which less strict criteria. Then the chance is higher. I had a paper gone back and forth for two years until accepted in another journal. In your PhD application cover letter and CV, you should mention your paper and state it is under review. Not all PhD applicants (and even graduates) have publications.

You can put studying what is required immediately as a priority while spending (at least) two hours a day in refreshing the fundamentals. In my field, I found that the fundamentals are almost everything. In industry interviews, I was only asked about the fundamentals. Also having solid theoritical background would help in presentations and viva and improve your image in front of colleagues.

It looks like a soft rejection. In UK they used to say they have no funding for non EU applicants. It looks like the US version

I am sorry for hearing you had this horrible cold harted experience. If supervisors are not to support their PhD students, then of what use are they?
Having a prominent academic and a distinguised professor in the panel was not the best idea. Your supervisors should not have done that from the first place. They are academics who rarely like any work and are very hard to impress.
I would recommend to fight for the PhD and try as much as you can to prevent the downgrade to MPhil. In the meantime, you could take a short break (a week or two). It is also not a bad idea to start looking for another PhD just in case.

I would recommend that you reply thanking him briefly for his feedback. Then follow the "official" recommendations from the journal reviewers and look at his personal recommendation if they are different from what he wrote offcially and try as much as possible to follow them. It is not nice I know but this is life. Not everyone knows how to express his opinion nicely.